1. Field of the Invention
The present invention relates to an oil passage structure of an engine of vehicle, particularly motor-bicycle or the like, which has a piston reciprocating in each of a plurality of cylinders, a crankshaft rotatably supported in a crankcase, and a connecting rod coupling each piston to the crankshaft.
2. Description of the Related Art
For engines, particularly those having four or more cylinders, there has been known a method of stabilizing, in an oil passage structure of a crankshaft, oil feed to big ends of connecting rods which are supported by plain bearings, such as providing an oil feed port to the end of the crankshaft, so as to configure the oil passage towards the big ends of the connecting rods as independent paths.
Japanese Laid-Open Patent Publication No. 2006-299830 discloses an analogous oil passage structure in this sort of engines.
In the conventional techniques, it has however been necessary to configure a relatively long oil passage in the crankshaft. Accordingly, the air undesirably remain therein may cause so-called air entrainment if no countermeasure is taken, and may seize the big ends of the connecting rods.
Substantially no consideration is paid on a viewpoint of air bleeding in the structure described in Japanese Laid Open Patent Publication No. 2006-299830.